2. Physiology
Dietary iodine is absorbed by GI, converted to iodide ion and
actively transported into the thyroid gland. The end result is two
hormones-triiodothyroxine T3 and thyroxine T4. Although the gland
releases more T4 than T3, the latter is more potent and less protein
bound.
Most T3 is formed peripherally from partial deiodination of T4.
3. Thyroid hormone T3 increases carbohydrate and fat
metabolism and is an important factor in determining
growth and metabolic rate. An increase in metabolic rate is
accompanied by an increase in O2 consumption and CO2
production,,increasing minute ventilation. Heart rate and
contractility are also increased,,from an alateration in
adrenergic-receptor physiology , not from increase in
catecholamine concentrations.
4. Hyperthyroidism
Clinical syndrome which results from exposure of the body
tissues to excess circulating levels of free thyroid
hormones. More commons in female.
Causes of Hyperthyroidism :
1. Graves’ disease
2. Toxic multinodular goitre
3. TSH secreting pituitary tumors
4. Toxic thyroid adenoma
5. Over dosage of thyroid replacement hormone
6. * Neuromuscular :
• Muscle weakness
• Hyperactive reflexes
• Nervousness
• Fine tremor
• Periodic paralysis
* Diagnosis:
The diagnosis of hyperthyroidism is confirmed by abnormal TFT,
which may include an elevation in serum T4 and serum T3 and a
reduced TSH level.
8. Anesthetic Consideration
A) Preoparative:
Manifest hyperthyroidism increases the risk of perioperative complications
and is a contraindication for elective surgery, with the exception of
thyroidectomy as measure of last resort when conservative treatment has
failed to control the condition.
HISTORY AND EXAMINATION Thyroid hormone status should be evaluated in patients
with goitre. Goitre alone is most often associated with iodine-deficiency hypothyroidism,
but may also be present in patients with hyperthyroidism. The patient must be examined for
signs and symptoms of increased thyroid function. The neck should be inspected and the
presence of stridor on forced inspiration noted. Engorged jugular veins can indicate
retrosternal goitre.
9. INVESTIGATIONS Patients with suspected hyperthyroidism require determination of
T4, FT4, T3 and TSH in addition to routine laboratory data. Elevated hormone levels
may exist without clinical signs of hyperthyroidism. Chest and neck X-rays will show
the position of the trachea and reveal any compression or deviation caused by
goiter. Retrosternal goiter usually does not interfere with intubation even when the
trachea is displaced. Indirect laryngoscopy is performed preoperatively by many
surgeons to document vocal cord function. CT scan and MR scans can reveal the
magnitude and extent of tracheal stenosis.
10. All elective surgical procedures, including subtotal
thyroidectomy, should be postponed until the patient is
euthyroid with medical treatment. The patient should
have normal T3 and T4 and should not have resting
tachycardia. Antithyroid medications and beta adrenergic
antagonist are continued through the morning of surgery.
11. B) Intraoperative:
* Premedication and anxiety.
*Cardiovascular function and body temperature should be closely
monitored In patient with a history of hyperthyroidism.
*Drugs that stimulate sympathetic nervous system should be
avoided because of the possibility of increasing blood pressure and
heart rate. Ex. Ketamine, Pancuronium, Atropine, Ephedrine.
*Thiopental may be induction agent of choice as it possess
antithyroid activity at high doses.
12. *Adequate anaesthetic depth should be obtained prior to
laryngoscopy or surgical stimulation to avoid tachycardia,
hypertension, ventricular dysrhythmias.
*Anticipate exaggerated hypotensive response during induction as
patient may be hypovolemic .
*Eye protection .
*Muscle relaxants can be given safely.
*Patients with autoimmune thyrotoxicosis are associated with an
increase risk of myopathies and myasthenia gravis.
* Reversal with glycopyrrolate instead of atropine .
14. Thyroid Storm:
*Thyroid storm is most serious problem .
*Characterized by: hyperpyrexia, tachycardia, altered consciousness,
and hypertension .
*Precipitating factors: infection, trauma, surgery.
*Onset is usually 6-24 hours after surgery, but can happen
intraoperatively mimicking malignant hyperthermia .
15. Treatment:
ABC guideline
* Patient will be managed in Surgical ICU
* IV Hydration, cooling of patient
* IV Propranolol(0.5mg increments) /esmolol to control heart rate
until less than 100.
* Propylthiouracil 250mg 6 hourly orally or by NG tube .
* Sodium Iodide 1 gram over 12 hours correction of any precipitating
events (infection) .
* Cortisol is recommended if there is any coexisting adrenal gland
suppression .
* Mortality rate is approximately 20% .
16. *Recurrent laryngeal nerve palsy:
Unilateral – hoarseness Bilateral – stridor
*Hematoma formation : May cause airway compromise -
required immediate opening of neck wound .
*Hypoparathyroidism : May result from unintentional removal of
parathyroid glands. Hypocalcemia will result within 24-72 hours.
17. Hypothyroidism
Impaired secretion of thyroid hormones or under
activity of the thyroid glands leading to
hypometabolic state-
- A high TSH level
- A low Free T4 & T3 level in serum
- A low total T4 & T3 level
18. Causes of Hypothyroidism
1. Primary hypothyroidism
2. Autoimmune (Hashimoto’s thyroiditis)
3. Post thyroidectomy
4. Post radioactive iodine
5. Over dosage of antithyroid medication
6. Iodine deficiency
7. Secondary hypothyroidism (failure of the hypothalamic-
pituitary axis)
23. Medical Treatment
1. Replacement therapy with thyroxine - Start with a dose
of thyroxine 50 micgm / day for 3 weeks followed by -
100micgm / day for 3 weeks - Finally 150 micgm / day
single daily dose.
2. Follow-up : Clinical checkup, serum TSH & T4 level
24. Although elective surgery is best postponed until a euthyroid state is achieved,
patients requiring urgent or emergent surgery may proceed with surgery if they
have mild or moderate hypothyroidism
25. Anaesthetic consideration
# Euthyroid state is ideal.
# Continue thyroid replacement medication on morning of surgery.
# Aspiration prophylaxis – due to delayed gastric emptying times.
# Sedative & narcotic administered more cautiously - more prone to drug
induced respiratory depression.
27. Intraoperative
# Patients are more sensitive to hypotensive effects of
anesthetic agents because:
1. Decreased cardiac output
2. Blunted baroreceptor reflexes &
3. Decreased intravascular volume
28. # Ketamine or Etomidate may be induction agents of
choice
# Succinylcholine and non-depolarizing muscle relaxants
are generally safe for use.
# Used peripheral nerve stimulator for monitoring muscle
relaxant.
29. # Controlled ventilation is recommended as patients tend
to hypoventilate
# Hypothermia occurs quickly
# Hematological (anaemia, platelet, coagulation
dysfunction) disorder
30. # Electrolyte imbalances
# Hypoglycemia is common
# Extubation/Emergence may be delayed secondary to hypothermia,
respiratory depression, or slowed drug metabolism
31. Postoperative
# Try to maintain normothermia
# Cautiously administer Opioids ,Consider regional techniques or
Ketorolac for pain control
32. Emergency
Myxedema Coma
# Rare form of decompensated Hypothyroidism
# Medical emergency with mortality rate of
15- 20%
# Infection
# CNS depression - especially in elderly
33. Characterized by
- Stupor or coma
- Hypoventilation
- Hypothermia
- Bradycardia
- Hypotension,
- Severe dilutional hyponatremia (SIADH)
- CHF
34. Treatment
# IV thyroxine is indicated (L-thyroxine loading dose 300-500ug,
followed by 50ug/day for 24-48hrs).
# IV hydration with dextrose containing crystalloid .
# Correction of electrolyte abnormalities.
# Support cardiovascular and pulmonary systems as necessary .
# Stress dose steriod.
# Avoid sudden warming.
